Ten-year worldwide study links mobile phone use to cancer (The Daily Mail)Prolonged use of mobile phones over many years could increase the risk of cancer, scientists have found.

However, a landmark study by the World Health Organisation into the safety of mobiles is expected to stop short of concluding that they definitely cause cancer - because the evidence is not conclusive enough.

And, despite spending £15million investigating handsets over the past decade, the authors will admit there is a need for further research into their health effects before definitive advice can be given.

The WHO's report will not be released until later this week, but two national newspapers reported yesterday that it will quote evidence saying people who use mobile phones for at least 30 minutes a day for 10 years have a greater risk - perhaps as much as a third higher - of developing brain cancer.

The 'Interphone' research has been carried out over the past 10 years in 13 countries, and is the largest of its kind.

Although it is known that radiation emitted by mobiles is absorbed by the head when it is held to the ear, it has not been proved that frequent use damages health - mainly because mobile phones have not been widely used for very long.

Between 2000 and 2004, researchers interviewed almost 13,000 people - both tumour sufferers and those in good health - to see if their mobile phone use differed.

Some of these studies have been published individually and have shown an increased risk of glioma - the most common type of brain tumour - for those who talk on their mobile for 30 minutes a day for 10 years.

Many saw the tumour develop on the same side of the head as they use their phone.

A summary of these results concluded: 'Pooling of data from Nordic countries and part of the UK yielded a significantly increased risk of glioma related to use of mobile phones for a period of 10 years or more on the side of the head where the tumour developed.'

But there are huge question marks over the reliability of the data. For example, its definition of 'mobile phone user' includes people who only made one call a week.

And there are also questions over how much can be gleaned from asking people years later how often they used their phone and what ear they held it to.

Another possible flaw is so-called 'recall bias', in which people who have a brain tumour retrospectively decide their cancer must have been caused by something - such as their handset.

There is also huge scepticism about another of the findings of the study: that short-term mobile phone use actually protects against cancer. Even the authors believe this is highly unlikely.

The report will call for more research, especially among the young.

The Interphone study is eagerly awaited by governments across the world and also by the mobile phone industry, which funded a quarter of the costs of the report.

The Department of Health has not updated its guidance for more than four years. It suggests children should be 'discouraged' from making 'non-essential' calls - while adults should 'keep calls short'.

Other countries go further: urging people to buy hands-free sets, sending texts rather than making calls, or banning the advertising of phones at children.